1. Field
The present invention relates to medical devices and medical methods. Specifically, the present invention relates to methods and systems for accessing a pericardial space and preventing strokes arising from a left atrial appendage (“LAA”) by achieving a complete occlusion of the LAA using an epicardial approach without creating a puckering of the LAA ostium.
The LAA is a cylindrical, ear-shaped, and sometimes tortuous and pedunculated muscular pouch projecting from the upper anterior portion of the left atrium of the heart. The LAA is a long, tubular, hooked structure and has a narrow junction with the venous component of the atrium. Thus, the LAA lies within the pericardial space, and is an extension of the left atrium. The pericardial space is also commonly known as the pericardial cavity and thus, both terminologies are used synonymously herein. The LAA functions as a decompression chamber during left ventricular systole and during periods when left atrial pressure is high. The LAA is also commonly known as the left auricular appendix, the auricular, or the left auricle. The left atrium receives oxygenated blood from the lungs by way of the pulmonary veins, and pumps the oxygenated blood into the left ventricle via the mitral valve. The LAA is more distensible than the rest of the left atrium and for a given increase in pressure, expands more than the left atrium. In virtually all patients, the LAA has muscle bundles termed pectinate muscles that are more than 1-mm thick with deep crevices or recesses in-between. In addition, in the majority of hearts, distinct protrusions from the LAA body termed lobes are also present within the LAA. The LAA structure has received increasing attention over the past 15-20 years due to its propensity to be a site of blood clot formation especially in patients with atrial fibrillation (“AF”). AF is the most common cause of strokes arising from the heart.
AF patients have a five-fold increased risk of an embolic stroke resulting primarily from thromboembolic events. There is very strong evidence that strokes which occur in AF are thromboembolic, such as, a blood clot which formed in the heart and then breaks off and travels to the blood vessel in the brain. In non-rheumatic AF patients, the stroke-causing thrombus originates almost exclusively from the LAA. Typically, the thrombus formed in the LAA break away from the LAA and accumulates in other blood vessels, thereby blocking blood flow in these blood vessels, and ultimately leading to an embolic stroke. Cardio-embolic strokes related to AF are large and prone to early recurrence with higher mortality. An antithrombotic or anticoagulant drug is one that suppresses, delays, or nullifies blood coagulation. Treatment with antithrombotic agents, such as warfarin, has been the “cornerstone” of medical therapy for these AF patients, but it can be difficult to maintain dosage within the therapeutic range and administration requires frequent monitoring and dose adjustments. Moreover, anticoagulants are associated with undesirable side effects, many of which are exacerbated with advanced age. As high as 50% of elderly patients are not offered anti-coagulation therapy even though they are at the greatest risk of development of embolic strokes. Therefore, alternative management strategies have been proposed, especially for the elderly, depending on the severity of the condition.
As such, the source of the blood clot must be identified to prevent recurrences and thus provide effective alternative therapy. It has been established that AF-related emboli originate primarily in the LAA. Based on this knowledge, procedures have been developed where the LAA is obliterated or excised and thus excluded from the systemic circulation. The aim is to prevent or inhibit thrombi in the LAA from embolizing into the systemic circulation. These procedures include (a) surgeries where the LAA is stapled with an amputating stapling device or sutured closed and/or excised and (b) endocardial procedures where an occlusive device is placed inside the LAA. Both approaches have been successful and are being tested, but also have very significant limitations.
Using stapling and similar technologies to exclude the LAA is often associated with incomplete closure leaving behind a stump. This stump can often serve as a source of future embolism. Similarly endocardial devices also have their share of problems. First, accurate placement of an endocardial device is highly dependent on the anatomy of the LAA, which is unpredictable because the shape and size of the LAA can vary widely. Other limitations of endocardial devices include the use of fixation barbs which can traumatize the LAA wall and incomplete occlusion due to gaps between the endocardial device and the LAA wall. There is also the possibility that the endocardial device may be by itself thrombogenic and it is constantly in contact with left atrial blood. A clip or a suture that is placed outside the heart does not come into contact with blood in the LAA cavity, and is less impacted by the LAA anatomy. The novel technology presented in this invention allows a puncture from the LAA onto the pericardial space in a controlled setting without the development of hemorrhage into the pericardial space. Following this, a catheter is exteriorized and over this, a closure device is inserted via the pericardial space that then clamps shut the LAA ostium.
2. Description of the Related Art
A number of approaches for plugging the LAA with an implantable device delivered via an endovascular approach have been proposed. In particular, occlusion of the LAA is believed to decrease the risk of an embolic stroke in non-valvular AF patients. By occluding the LAA, the thrombus formed in the LAA are unable to migrate to other blood vessels, thereby reducing the risks of thromboembolism and embolic stroke. Hence, the occlusion of the LAA is believed to be an effective stroke prevention strategy in non-valvular AF patients. Indeed, this concept of occluding the LAA as a stroke prevention strategy is being increasingly tested with implantable medical devices that occlude the LAA using an endocardial and epicardial approaches.
An example of an endocardial approach is the WATCHMAN device developed by Atritech Inc. (located in Plymouth, Minn.). The WATCHMAN device is an implantable device designed to occlude the LAA in non-valvular AF patients. The WATCHMAN device is delivered to the LAA via an endovascular approach and is placed distal to the LAA ostium, which upon expansion, occludes the LAA. The occlusion of the LAA prevents the migration of the thrombus formed in the LAA, thereby reducing the risks of thromboembolism and embolic stroke. In the WATCHMAN device's clinical trial, PROTECT-AF, the results showed that in AF patients who were candidates for warfarin therapy, the closure of the LAA using the WATCHMAN device was associated with a reduction in hemorrhagic stroke risk as compared to warfarin therapy. Additionally, these results showed that all-cause stroke and all-cause mortality outcomes were non-inferior to warfarin.
However, the WATCHMAN device's “one size or one shape fits all” approach results in several limitations, such as inadequate circulatory exclusion of the LAA. For example, a major limitation of the WATCHMAN device is the incomplete occlusion of the LAA because it is relatively common for there to be a gap between the WATCHMAN device surface and the LAA wall. These gaps are more likely to enlarge over time and persist, while new gaps also occur during follow up. Gaps are also commonly noted to enlarge over time, and new gaps occur during follow up even if the LAA was completely sealed at implantation. The long, tortuous and pedunculated structure of the LAA can make it difficult to seat the device within the LAA cavity. This can result in the device placed in a suboptimal manner with incomplete occlusion, and an incomplete occlusion is worse than no occlusion. The present invention provides for more refined systems and methods for achieving a complete occlusion of the LAA.
Another limitation of the WATCHMAN device is the fixation of barbs or wires engaged in the walls of the LAA. As shown in the WATCHMAN device's PROTECT-AF trial, major adverse events include bleeding and pericardial effusion. Pericardial effusion is the abnormal accumulation of fluid in the pericardial cavity, which can negatively affect heart function. The present invention provides for more refined systems and methods for achieving a complete occlusion of the LAA without the risks associated with tears or bleeding arising from the fixation of barbs or wires engaged in the LAA walls and without implanted hardware that is constantly exposed to blood in the LAA cavity.
More recently, EpiTek Inc. (located in Bloomington, Minn.) and SentreHEART, Inc. (located in Redwood City, Calif.) have each developed implantable devices designed to occlude the LAA. The SentreHEART, Inc.'s device is called the LARIAT. These devices are introduced percutaneously into the pericardial cavity, also known as the pericardial space, and then used to place a suture circumferentially at the ostium of the LAA, typically referred to as LAA ligation. Pericardial access is typically established via a subxiphoid approach with a needle. A wire is placed through the needle into the pericardial cavity. A sheath is then placed in the pericardial space through which a catheter is advanced to the desired location. The procedure of obtaining pericardial access with a needle via a subxiphoid approach can be technically difficult, and associated complications include lacerations of the myocardium, the coronary arteries and veins. Unlike the Epitek device, the LARIAT device also involves placement of a balloon within the LAA. Using magnetic forces, the wire within the pericardial space and the balloon in the LAA are made to come into contact. A pre-tied suture that is placed around the LAA is advanced from the exterior over the wire and balloon and then tightened. Due to the severe technical limitations associated with the procedure, it has not been adopted in a widespread manner. The present invention provides for an anchoring hemostatic mechanism that makes the procedure of accessing the pericardial space safer and less difficult.
LAA ligation from a circumferentially applied suture or tie also suffers from puckering of the occlusion which can compromise sealing. In addition to causing a puckering and incomplete occlusion of the LAA ostium, a circumferential suture also has the disadvantage of having a potential to cause a tear or laceration of the LAA. It is anticipated that in the elderly hearts (the elderly patients are the primary candidates of this approach), which are known to be delicate, this approach may be associated with an even greater risk of bleeding and tears. In the event of a tear of the LAA in the elderly hearts, there is a high likelihood of this being fatal. This is an emergent situation and there will not be time to transfer the patient to the operating room. The present invention provides for more refined systems and methods for achieving a complete occlusion of the LAA without creating a puckering effect.
For the foregoing reasons, there is a need for novel technology to achieve a complete occlusion of the LAA without creating a puckering of the LAA ostium. The present invention addresses this need by presenting methods and systems for achieving a complete occlusion of the LAA using an epicardial approach without creating a puckering of the LAA ostium.
Additionally, within the last decade, there has been an increasing use of a surgically deployable metallic clip that can be place around the base of the LAA. The most prominent among these is the AtriClip manufactured by AtriCure Inc. (located in Cincinnati, Ohio) described in U.S. Patent Application Nos. 2006/027553 and 2009/051270. The AtriClip is made of two parallel rigid titanium tubes with elastic nitinol springs covered with a knit-braided polyester sheath. Deploying the AtriClip is a surgical procedure that requires the chest in between the ribs to be cut open rather than a puncture and is placed over the LAA under direct visualization. It is not a minimally invasive procedure that is necessarily performed by the surgeon rather than the cardiologist.
Methods and apparatus for accessing a pericardial space and optionally placing an external closure over the LAA are described in U.S. Pat. Nos. 6,423,051; 7,951,069; and U.S. Patent Application No. 2011/276,075 (“the '075 Application”).
The present invention is distinguished from the aforementioned references for at least the following reasons. In particular, the '075 Application only discloses a single occlusion member to occlude the LAA that is then followed by an intentional perforation of the LAA to obtain access to the pericardial space. The catheter is then exteriorized and using the exteriorized catheter as a railing, a suture is delivered to ligate the LAA. Moreover, the '075 Application only discloses an occlusion member inflated within the LAA, in which this one inflated balloon is used to occlude the entirety of the LAA cavity. By contrast, the focus of the current invention is to limit or eliminate blood flow through the neck-like ostium of the LAA. This is achieved by the expansion of a plurality of inflatable balloons immediately across the LAA ostium both within the LAA and in the left atrial cavity. The LAA wall has thick muscle bundles that are more than 1-mm thick with deep recesses in-between the bundles, giving it a rough appearance. Protrusions from the LAA wall termed lobes are also seen in the majority of the hearts. Due to these recesses and lobes, a single occlusion member within the LAA cavity is unlikely to provide an effective hemostatic seal. By contrast, the present invention presents a plurality of inflatable balloons to provide an effective hemostatic seal.
In the present invention, the main occluding element is deployed within the cavity of the left atrium, rather than within the LAA. This main occluding element, such as an inflatable balloon, has dimensions larger than the LAA ostium when inflated. Thus, when inflated, this main occluding element envelops the LAA ostium. This main occluding element's surface is in contact with the smooth surface of the left atrial cavity wall and upon full deployment, is able to provide an effective hemostatic seal.
The primary purpose of the expandable elements that are within the LAA, rather than to achieve a hemostatic seal, is to pull the left atrium cavity balloon towards the LAA ostium (by application of electromagnetic forces) and to jam it shut. In an exemplary embodiment, the present invention has the presence of thin tubes attached to the balloon surface of the left atrium cavity balloon. These tubes allow for the application of vacuum or suction forces that will be applied against the smooth-walled left atrium to allow for a more effective hemostatic seal.
The use of multiple inflatable balloons to create a tight hemostatic seal for occluding the LAA ostium is not presented in the prior art. In particular, at least one of the inflatable balloons occluding the LAA ostium is non-compliant, such that upon inflation of the non-compliant balloon, the surrounding LAA walls are expanded to accentuate the constriction that one would expect at the LAA ostium. The use of these multiple inflatable balloons distinguishes the present invention from the prior art's single occlusion element that is placed within the LAA cavity. Hence, the present invention should not result in gaps between the occlusion element's surface and the LAA walls. Second, the use of electromagnetic coils within the inflatable balloons, wherein upon inflation of these balloons, the electromagnetic coils also expand within these balloons, is not present in the prior art. These electromagnetic coils further enhance the hemostatic seal by way of electromagnetic forces between the inflated balloons occluding the LAA ostium. The use of the electromagnetic coils ensures that the present invention does not result in gaps between the occlusion element's surface and the LAA walls.
Another novel feature of the present invention is the coating of the inflatable balloons with biocompatible hydrogels to provide a superior seal. Also novel is the presence of tubules attached primarily to the left atrial cavity balloon will allow for the vacuum or suction forces that are applied from an external source. This will result in the left atrial and LAA tissues adhering to the balloons more effectively, thus resulting in a superior seal.
The present invention's closure device comprising of a suture looped around two semi-rigid tubes further distinguishes the present invention from the prior art. The present invention's closure device ensures that there shall be no puckering effect around the LAA ostium commonly seen in the prior art, such as with the devices developed by EpiTek Inc. and SentreHEART, Inc. Additionally, the coating of hydrogel or silicone to the interior surfaces of the two semi-rigid tubes is another novel feature, ensuring that there is no puckering effect. Moreover, an anchoring balloon attached to the exteriorized catheter used to stabilize the LAA while the closure device is being deployed to the LAA ostium is yet another distinguishing novel feature. This anchoring mechanism ensures that the exteriorized catheter, when pulled externally is able to have its proximal end within the LAA cavity, after the hemostatic balloons have been deflated and removed. Furthermore, the present invention provides for an injuring step that is not present in the prior art. Specifically, the injury step is designed to induce to induce a tissue response that enhances the closure and sealing of the LAA ostium.
The present invention can also be used for other purposes to canulate the pericardial cavity. In case it is decided to not occlude the LAA ostium at the end of the procedure, the site of puncture in LAA can be sutured closed with an absorbable or non-absorbable suture (with or without a collagen pledget) applied from the exterior.
It is also anticipated that the present invention can be used to occlude or ligate any tubular structure (vascular or otherwise) within the body (for example an aneurysm).
Underlying Principles of the Present Invention
Unlike the right atrial appendage which has a broad based pyramidal shape, the cylindrical pedunculated shape of the LAA and the presence of a narrow waist or constriction at the LAA ostium allows this structure to be occluded by the placement of expanding elements within or adjacent to the LAA. The LAA is also more compliant compared to the left atrial cavity allowing for balloons to be inflated within the LAA.
Occluding the LAA allows for the controlled puncture of the LAA where access to the pericardium can be obtained from the left atrial cavity, without any bleeding occurring into the pericardial space. The catheter that is placed in the pericardium can now puncture the parietal pericardium and be exteriorized for example in the subxiphoid region. This can be used to deliver materials and devices to the pericardial space in a safe manner.
However, inflating a cylindrical balloon within the LAA is unlikely to provide a safe and stable hemostatic occlusive seal for the following reasons. The first reason is the presence of pectinate muscles and lobes in the LAA. Nearly all adult LAAs contain pectinate muscles that are greater than 1-mm in diameter. As a result of these pectinate muscles, the LAA has a rough quality unlike the left atrial cavity, which is smooth-walled. Deep recesses are present in the LAA in-between these pectinate muscles. The LAA also has the presence of larger distinct protrusions termed lobes. The presence of these lobes and recesses makes it difficult for a single balloon inflated within the LAA to provide an effective seal since the cavity of the lobes and the recesses would allow for blood through flow through.
In some hearts, a distinct constriction is absent at the ostium of the LAA. In some atria, the constriction when present at the LAA ostium is not circumferential. This raises the possibility that upon inflation of a single balloon within the LAA, this inflated balloon may fall out of the LAA into the left atrial cavity.
The novel invention presented in this application solves the above mentioned problems through the following innovations illustrated by the hour-glass concept.
The Hour-Glass Concept.
The Hour-Glass concept presents the importance of multiple inflatable balloons in controlling the neck of the hour-glass. One of the key factors affecting the time measured in the hour-glass is the neck width. The neck of the hour-glass represents the LAA ostium. The top bulb of the hour-glass represents the left atrial cavity while the bottom bulb of the house-glass represents the LAA. This hour-glass concept as it relates to the LAA was conceived by the named inventor on this patent application.
The current invention is based on the concept that preventing the sand or water flowing from the top bulb to the bottom, which is achieved by occluding or sandwiching the neck by a combination of inflatable balloons that are deployed across the constriction and forced towards each other rather by inflating a single balloon in the bottom bulb only. These inflatable balloons that are placed immediately across the neck are approximated towards each other by a combination of pushing and pulling, as detailed in FIGS. 17-18. A first balloon is inflated within the LAA adjacent to the LAA ostium and a second balloon is inflated within the distal portions of the LAA. The inflated second balloon pushes the inflated first balloon towards the neck of the hour-glass, which represents the LAA ostium. The inflated first balloon is also pulled towards the neck of the hour-glass by manual traction on the inner sheath.
A third balloon is inflated within the left atrial cavity adjacent to the LAA ostium. Electromagnetic coils can also be present within the first and the third balloon. The electromagnetic coils in the inflated third balloon also pull the inflated first balloon towards the neck of the hour-glass by way of electromagnetic forces. Conversely, the electromagnetic coils in the inflated first balloon pull the inflated third balloon towards the neck of the hour-glass by way of electromagnetic forces. Thus, the main function of the inflated first balloon is to pull the inflated third balloon towards the LAA ostium by way of electromagnetic forces. The main function of the inflated second balloon is the push the inflated first balloon towards the LAA ostium.
The present invention presents the accentuation or exaggeration of the LAA ostium by inflating a non-compliant balloon within the LAA adjacent to the LAA ostium. The first inflatable balloon is non-compliant and inflated with higher pressure. A non-compliant balloon is likely to deform the LAA walls and by creating expanding the LAA walls, it will accentuate the neck of the hour-glass and allow for a better approximation of the inflated balloons against the surfaces. (Hoit B D, Walsh R: Regional atrial distensibility. American Journal of Physiology 1992; 262:H1356-H1360). The LAA is more distensible than the left atrial cavity and hence should readily deform especially in response to high pressure inflation with a non-compliant balloon. The inflated non-compliant first balloon is then forced towards the LAA ostium by a combination of pushing and pulling.
The second balloon is largely compliant and is inflated within the distal portion of the LAA. Upon inflation, the second balloon conforms to the LAA anatomy and pushes the inflated first balloon further towards the LAA ostium, as shown on FIGS. 17-18. Additionally, the inflated second balloon prevents the inflated first balloon from being pushed away from the LAA ostium.
The third balloon, which is located on the outer sheath, is inflated within the left atrial cavity adjacent to the LAA ostium and is pushed towards the LAA ostium. Thus, the inflated third balloon envelops the LAA ostium. The inflated first and third balloons are manually pushed towards each other by pulling on the inner sheath and pushing on the outer sheath.
The present invention guards against the possibility of the inflated first balloon falling out of the LAA and into the left atrial cavity. In particular, the inflated third balloon has an additional function of preventing the inflated first balloon from falling into the left atrial cavity especially in the setting of an indistinct LAA ostium where a constriction is absent. Additionally, a locking mechanism is described where the inner and outer sheaths lock on to each other. This locking mechanism may be present intravascular, intracardiac, or outside the body. In addition, an additional inflatable balloon that is attached to the outer sheath can be inflated immediately to the left of the interatrial septum to render the outer sheath stationary.
The LAA ostium has an oval shape. Applying a circumferential tie or suture to the LAA ostium is going to compress a fixed circumference to a smaller area and therefore will cause puckering. Puckering is more likely to cause gaps and incomplete occlusion. A suture is also more likely to cause tears in the LAA especially in elderly hearts. A closure device that approximates the opposing surfaces is a better approach and is unlikely to cause puckering. The present invention presents a novel closure device that approximates surfaces opposite to each other and brings them into contact is a better approach. This is most effectively created by applying forces along the short axis or short diameter of the oval or elliptical ostium. Hence, a barrette or clip applied at the ostium of the LAA is more likely to seal off the structure. Force applied along the long diameter is less likely to approximate the opposite surfaces since (a) the two surfaces will have to travel a longer distance and (b) a greater amount of force will be necessary to overcome the intrinsic tissue elasticity.
Creating endothelial denudation at the LAA ostium by intentional injury will create inflammation and cross-linking of collagen fibers, resulting in more durable occlusion of the LAA ostium. The present invention provides such a feature. For example, endothelial denudation at the LAA ostium can be created by application radiofrequency (RF) current via the inflatable balloons at the LAA ostium.